Synthesis Of Amphiphilic Heteroarm Star-Shaped Polymer By The Use Of Polyfunctional Chain-Transfer Agent Via Conventional Free Radical Polymerization

Amphiphilic heteroarrn star-shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in three steps.Firstly,conventional free radical polymerization of methyl methacrylate(MMA)initiated by 2,2'-azobis(isobutyronitrile)(AIBN)was carried out in the presence of polyfunctional chain transfer agent,pentaerythritol-tetrakis (3-mercaptopropinate)(PETMP).At appropriate monomer conversion, two-arm star-shaped s-PMMA having two residual thiol groups at the chain center was obtained.Secondly,the s-PMMA obtained above was used as macro-chain-transfer agent for free radical polymerization of ten-butyl methacrylate(tBMA).With the increase of tBMA conversion, the number-average molecular weights of the crude products shifted to higher molecular weight direction.Furthermore,their molecular weight distribution curves were unimodal through out the polymerization process. At appropriate monomer conversion,the heteroarm star-shaped polymer with two PMMA arms and 1.6 PtBMA arms was obtained successfully. Finally,cleavage of the tert-butyl ester groups was achieved by treating the heteroarm star-shaped polymers in dichloromethane with trifluoroacctic acid at room temperature.The ~1H-NMR spectrum of hydrolyzed product showed that the terl-butyl protons of the PtBMA disappeared complctely,indicating that the PtBMA chains had successfully transformed into poly(methylacrylic acid)(PMAA)chains.The self-assembly behavior of the amphiphilic heteroarm star-shaped polymer in 1%KOH were investigated.Transmission electron microscopy(TEM)and dynamic fight scattering(DLS)were used to characterize the sizes and size distributions of the aggregates of the hydrolyzed product.Futhermore,conventional free radical polymerization of tBMA initiated by AIBN was carried out in the presence of polyfunctional chain transfer agent,PETMP.At appropriate monomer conversion,the s-PtBMAs having definite residual thiol groups at the chain center were obtained.The s-PtBMAs obtained above were used as macro-chain-transfer agent for free radical polymerization of MMA and styrene.